Method of making benzene hexachloride



May 15, 1951 K. c. KAUER ET AL METHOD OF MAKING BENZENE HEXACHLORIDE Filed Sept. 6, 1946 INVENTORS Lanna-H's C. lLaubr Francis U. Mquid' Edgar C b i'H'on M M Patented May 15, 1951 l METHOD OF MAKING. BENZENE HEXACHLORIDE .;;Kenneth C." Kauen'Francis N. Alquist, andEdgar :6. Britten, Midland, Mich., assignors .to :The

. Dow Chemical Company, Midland, Mich., a corporation of Delaware 'Application September 6, 1946; SerialNo'.*695,238

.4 Claims. 1 This .invention-relatestor a. method: for' the production. of benzene hexachloride; also: known as hexachlorocyclohexane,t CI-IsCle. Itrrelates in particular to a commericallypractical process for making this compound-inthedark; i. erwith- 1 out need for actinic radiations. "It isespecially concerned withsuch a method, theproduct. of which is. consistently rich in the gamma-isomer of benzene. hexachloride.

Various methods of making rbenzene hexachloride are-.known:intherart. These include the substitution chlorination-"of cyclohexane and the-addition chlorinationof benzene. The latter is generally conceded to be theamorepractical reaction. one of photocatalysis, employingmercury vapor lamps, "direct sunlight, or other sources of actinic radiation. as a catalyst for :the chlorination -reaction. If such a' processecan be avoided, many operatingdiflculties -Wll1- be overcome. Among these is the tendencyfor the: product to separate from the reaction medium as a solid, in the reactor. Some few. suggestions. have been made to employ chemical :catalysts; and to. effect "the chlorination in :dark equipment. Thus, various metal chlorides, dilute: sodium hydroxide,- water and dissolved .ethylene haveaallbeen-. suggested as, catalysts. It has also. been. disclosed to pass pure, drybenzene vapors and-.dry chlorine'over a. reduced copper catalyst, to.- produce --benzene hexachloride. Anothenprionprocess involves -the treatment of benzene withliquid-chlorine. =rSome of. these. methods are .commercially. impractical. Some of them form mixed addition.and.-1substitution products. .Others appear to give a product with a-very lowratiooithe gamma -isomer to the other isomers .present, .as...the.marketed product. contains, sometimes as..little.-as. 2-4 per cent. A, practical process, yieldingtconsistently high proportions of the insecticidally valuable gamma-isomer, is much to be-desired.

It. is :accordingly among the objects .of,.the present invention to, provide a. practical ..and economical process.v for the preparation. .ofbenzene hexachloride. .A related. objectris. .toprovide such-v a process from. which the..product. contains consistently. .from..10..to. ;.per vcent of: gammabenzene .hexachloride. .A:=further object ---is to provide; a process .as. aforesaid, capable of being operated. in the"; dark;-=and-in arcontinuous manner. Another object-is'to provide suchza process, in which. the:benzene'; hexachloride remains 'idissolvedin the reaction-,medium :to :arpractical .high concentratiomaand does an'ot separate asz-sclid in the reactor.

In-- common-practice theprocess is z We have now found a method whereby the foregoing and" related objects maybe attained. The new method comprises mixing liquid benzene withifrom 6 to 7 percent or more of its weight of chlorine in. the presence of small amounts of propylene, .and allowing this mixture to react at. a temperature between 5. and'theboiling point .of benzene, :more: economically not above C.,.and preferably. one between 35 and 45 "C.,' Withdrawing 'the'resulting solution from .the reaction zone before 'the" benzene hexachloride :produceda..'exceedsi;a' concentration; of .about 18 per cent'fln the' solution; and recovering benzene hexachloride from. 'ltSiSO'llltiOl'l in benzene and propylene. chloride. The" reaction is 2 most conveniently carried: outfinrthe darkybut is not adversely. affected-:by diffused light or by actinic'radiations. lnzits most practical form, the method 10f the invention'isa continuous one, and may be carried out-in'thezmanner hereinafter described-in detail.

We are i aware of "the" publication by" Stewart and Hanson, Journal of -:the American'-' Chemical Society, vol. 53, page 1121' (-1931) in which mention-is made of the production of benzene hexachloride when a solutionof chlorine in benzene is mixed with a'solution of ethylene in benzene. We have found, however, that-ethylene is not a satisfactoryrinitiator forthecommercial production of1.-benzene 'hexachloride,- for several reasons. --For example, the resultantmixture of benzene andethylene' chloride is a much poorer solvent for benzenehexachloride than'is benzene alone,:or than a mixture of benzene and propylene chloride. Further,- because-of the small difierence between the boilingpoints of benzene and ethylene chloride, these materials cannot lie-separated by commercially feasible' distillation technics. Accordingly, when attempting to-use ethylene as the catalyst for the present-reaction, it has been found that-the ethylenechloride concentration continues -to build-up, even""in cyclic systems, and the solubility -of benzene hexachloride .inthe reaction mixture continues todecrease correspondingly, making'it impossible to achieve a-practical rate of reaction-without encountering precipitation of solid benzene hexachloride and all of the-operatingdifiiculties inherent-in such a two=-phasemixture.

*In view: 'of the marked advantages .of propylene overkethylene as an initiatorlfor the present reaction, attempts have been made to use butylene and other .olfinic' compounds-"but Without success. 'Butene-lj'for' example, when substituted forrpropylenei in the reaction mixture; prod only 42 per cent as much benzene hexachloride per unit weight of chlorine input, as did propylene, and the product obtained contained from one-third to one-half the proportion of gamma isomer which is consistently obtained by the method of this invention. Such other unsaturates as vinyl chloride, perchlorethylene, and butadiene do not catalyze the reaction, and neither do the olefine chlorides, such as ethylene chloride and propylene chloride.

When operating according to the present invention, it is found that there is an initial induction period, during which little if any benzene hexachloride is produced. During this period the chlorine concentration builds up in the system to between 6 and 7 per cent by weight at temperatures near 40 0. Somewhat higher concentrations are obtained at lower temperatures. The chain reaction induced by the propylene then starts rather suddenly, with evolution of considerable heat, and the rate of chlorine input may be stepped up to provide enough chlorine for the accelerated reaction and to maintain a saturated condition in the benzene. Under these conditions, some chlorine passes through the system unchanged, but the maintenance of such a condition is fully justified by the greater rate of reaction which it induces. The passed chlorine may be recycled, if desired. The duration of the induction period and the vigor of the reaction both vary inversely as the temperature, other factors being equal. Thus, if the temperature in the reactor is kept between and C., the induction period is somewhat longer, and the reaction, when started, is more vigorous, than when the temperature is between 35 and 45 C. At the lower end of the operative temperature range, very eflicient control must be maintained on the chlorine supply and On the means for extracting the suddenly liberated heat of reaction. A slight advantage is found in operating at 5 to' 15 C., in the somewhat higher ratio of the gammato the other isomers, but the reaction is much more readily controllable, and a consistently high yield of gamma-benzene hexachloride is obtained at temperatures which range up to 60 0., but which are preferably between 35 and 45 C.

After initiation of the reaction, it is not necessary to maintain a flow of propylene at the initial rate, as a very low molar ratio of propylene to chlorine appears to sustain the reaction, and the propylene may even be shut off for a time without injurious effect on the yield or efficiency of the reaction. The ratio of propylene to chlorine may, but need not exceed 1 mol of the former for each 6 mols of the latter in the early stages of the reaction, and improved results are obtained in settled operation using a molar ratio in the range between 1:8 and 1:10. Ratios as low as 1:20 maybe used.

Having now described the process in general terms and given some of the preferred conditions of operation, a more detailed description will be given with reference to the accompanying drawing, wherein the single figure is a diagrammatic representation of an elevation of one form of apparatus for the continuous production of benzene hexachloride according to the new method.

Commercially dry benzene is introduced into the apparatus through valve Ill until it starts to overflow through valve H, which is then closed. Pump I2 is started, causing circulation of the benzene downward through tower l3 and upward through reaction tube Hi, the cycle, being come pleted through pipe 15. Tower l3 may be at least partially filled with packing rings I6, if desired. Chlorine and propylene are introduced in measured amounts into the circulating liquid I1 through separate inlet tubes 18 and I9, respectively, which are preferably located near the bottom of tower l3, to ensure complete absorption of the gases in the liquid. A portion of the cycle, and preferably pipe [4, is surrounded with a water jacket 20, for adjusting the temperature of the circulating mixture. When the reaction ha started, and sufficient chlorine has been introduced to provide an amount, preferably near 15 to 17 per cent concentration, of benzene hexachloride in the circulating liquid, valves l0 and H are each opened sufiiciently to bleed some of the reaction mixture continuously thereafter through pipe 2| into kettle 22, and to replace that volume of liquid with fresh benzene. Kettle 22 represents a still from which benzene and propylene chloride may be taken off in the overhead, and condensed as by condenser 23, and from which the benzene hexachloride may be withdrawn periodically, as through valve 24. The mixture of benzene and propylene chloride may be separated, as in a stripper tower 25, the propylene chloride being drawn off at the bottom through valve 26, while the benzene i vaporized and passes to condenser 21, from which a part is returned to tower 25 as reflux and a part is returned to the reaction system, through drier 28, if necessary. Absolute dryness of the benzene is not required, but a separate water phase should be avoided in the reaction zone, for best results. If desired, when an excess of chlorine is passing through the system, it may be separated from the mixture of benzene and propylene chloride, and returned to tower I3 through pipe 29. If desired, pump I 2 may be omitted, and natural circulation may be relied upon. In such case the cyclic flow is opposite to that shown in the draw ing.

The reaction is most conveniently carried out, and is most readily controlled in the dark, i. e. when run in nickel or other light-impervious metal which is not a catalyst for the substitution chlorination of benzene, or in ceramics or .darkened or wrapped glass apparatus. If it is desired to increase somewhat the possible rate of chlorine input, it is permissible to irradiate the reaction mixture in a portion of its cycle. This may be done conveniently through a section of glass pipe inserted, for example, in the section marked A.

It is to be understood that many other forms of apparatus may be employed instead of the one shown, and that the process is capable of being run batchwise or in a semi-continuous manner, instead of in the continuous manner described above.

The method of the invention produces a benzene hexachloride containing consistently from 10 to 15 per cent of the gamma-isomer, and usually about 13-14 per cent of this insecticidally active material, as wellas a predominant amount of the alpha-isomer and lesser amounts of the beta-, delta-, and epsilon-isomers, with traces of others as yet unidentified. The various isomers present and their respective amounts are most readily determined by infra-red analysis from calibrations made with the pure isomers.

The following examples illustrate the practice of the invention, but are not to be construed as limiting the same to the specific conditions de c ibed:

i the. present l'inve'ntion fi'Eidmpl i l'In emote-soon? earn-eater in V "40.3) ts -o weight, includingftl'idnitialc 7 ea and circulated ina reactiorfzone :iof 11'-"hours,-"with rigorous isg'ira'u "faction zone. 'fDuri'rig' this ti'me'ther wasthe reactor 1643 'parts'by weight 11 155'p'ms1by wfgl'it l flrnols) or ratio; of propyle e t ifc'h rine, was 1' to 6125. "The reaction empcrature .held-between 37. and 43 1p. I'Pr 'd' drawn and fresh benzene intfo'cl c maintaina single liq zone. f-Exces'schl'ori' by'wei'ght,- pa'ssd lt h the reactor and was cau'ghtdna special "'cold' trap. There-was recovered from'. =the -;reaction l0 parts by"weight of benzene hexachloride, contaimng 13.2 per cent "of gamma isomer. Allowingfi I 'e. herecovered and for that converted to- 'p opylne chloride, the statute-was '93 er cent efficient in producing benzene hexachlor de. No significant substitution chlorination occurr-ed'g as th arnount of hydrogen "chloride evolved was only 0.35 par by weight. Y

' phase"in "the reac In order to compare the resiilts 'obtained sing propylene from different sources, and when omitting propylene from the reaction, a series of small scale runs were made in a painted and tinfoilwrapped glass apparatus. The charge of benzene was the same in each case, and the duration of the run, the weight of chlorine and its rate of 35 100 pounds of benzene.

introduction, and the reaction temperature, were the same for all runs. The results are tabulated in the following table.

Benzene Gan Yield of Ben- Propylene, Tempera- Hexa- Isomer zene Hexa- Quality 1 ture, C. chloride, Per i chloride, Mol

Grams Per Cent 1 90 37-44 221 12 100 90 37-44 226 13. 2 100 100 36-43 130 15. 7 95 None 37-42 18 8 1 The 90 per cent propylene was a cracked petroleum product containing 90.6 per cent propylene, 3.2 per cent propane,;1.2 per cent allene, 3.1 per cent methyl acetylene, 0.9 per cent ethane. 0.3 per cent carbon dioxide and 0.7 per cent hydrogen sulfide. -The 100 per 50 cent propylene was from a cylinder of liquefied, purellnaterial.

2 In the runs using propylene, yield was calculated fro'mthc chlorine available after deducting recovered chlorine and chlorine equivalent to the propylene used, from total chlorine input. i

Example 3 In a completely darkened glass tubular reaction apparatus, 390 parts by weight of benzene was treated in the course of 4 hours with 450 parts by 7 weight of chlorine and 42 parts by weight of pure propylene (1 mol propylene to 6.3 mols chlorine). The temperature was initially 19 0.; but rose to and was controlled at 30 C. when the reaction started after a short induction period. About 75 65 was distributed about as follows:

U0 or the hlori'ne* passed through the t ge and was-cau'ght fiddiqufi'd ra edtr'a'p. There was obt'ainedm'm ms' of benzene heiiachl'oride, having about 13 er tem; of- -the' gamma product. After-allowing fo'r the recovered chlorine' and the chlorine" c'onverted to propylene chloridefitheyield ofbenzene hexachloride was 86 per cent of the "theoretical. flther T runs= have* shown -it to' be undesirable ="to haivewaterrpresentdma large enough quantity to form' aseparate liqi-iid phase in the-=system. Thus; :-in: two otherwise identical runs both using propylene from the same sourcefiwhen one-was Bib-n carried -out wi-tlr commercially dry benzene and the amount of parts the' oth'er with benzene containing 0.'25 per. cent 'niore Water-than requiredtdsaturate the 'benzene, the wet reaction produced only 0.'7-*as-much "benzene :hexachloride in-a given length oft-time as did the -dry* reaction. The -benzene=:hexachloride produced had, -in-=both cases, between -13 and-l4-=per cent of gamma-isomer.

Etrdmp'le'4 A =tubularreactor was: constructed from two t 325 lengths of glass pipe 14 feet long and 4 inches in diameter, connected near each end byiglass tubular "cross ln'embers one inch in diameter. Provisiorfwas "nlade' for the introduction or benzene "atthe"'top,' Ellid Of (5111011116 -211d1.")1613371'F5file"ll all the bottom of one of the larger pipes, and the other was provided with externally applied cooling by means of flowing water. The glass reactor was painted black and was wrapped or shielded to exclude light. The system was filled with Chlorine and 90 per cent propylene were bubbled into the benzene, and the liquid began to move upward in the uncooled leg and downward through the cooled leg of the cyclic system. The ratio of chlorine to benzene 40 was about 6 to 8 mols of chlorine for each mol of propylene. The solution first assumed the yellow-green color of dissolved chlorine and began to show signs of reaction when the solution had become saturated with chlorine. The reaction temperature was controlled near 35 to 45 C., with occasional variations in the range from 30 to C. The rate of chlorine input was adjusted so that about one-fourth of the chlorine passed through the system unreacted. This amount could have been, but was not, recycled. When 30 pounds of chlorine had been put into the system for each pounds of benzene, the chlorine flow was discontinued and propylene flow was continued until the solution again was colorless. The solution was withdrawn from the reactor and was heated to drive benzene and propylene chloride from the benzene hexachloride. The recovered benzene hexachloride weighed about 22.5 pounds and contained about 13 per cent 0 gamma-benzene hexachloride.

Similar runs in the same apparatus consistently produced a material containing from 10 to 15 per cent of the gamma-isomer. The chlorine employed in these runs, for each 30 pounds input,

Pounds Chlorine Input To benzene hcxachloride, 16.5. To propylene chloride, 6.0 Unrcacted 7.5

benzene in a closed system, bubbling thereinto an amount of chlorine sufiicient to keep the benzene saturated therewith and an amount of propylene sufiicient to initiate and to maintain the addition reaction between benzene and chlo rine, but not in excess of one mol of propylene for each 6 mols of chlorine, maintaining the temperature of the reaction between 35 and 45 C., to product benzene hexachloride, and continuously Withdrawing part of the circulating solution from the system and replacing it with a similar volume of benzene, to prevent the concentration of benzene hexachloride from reaching the saturation point in the circulating liquid.

2. The method which comprises circulating benzene in a closed dark system, bubbling thereinto an amount of chlorine suflicient to keep the benzene saturated therewith and an amount of propylene sufiicient to initiate and to maintain 8 the addition reaction between benzene and chlorine. but notin excess of one mol of propylene 'f or each-i6 mols of chlorine, maintaining the temperature of the reaction between 35 and f15 C., to produce benzene hexachloride, and continuously withdrawing part of the circulating solution from the system and replacing itwith a similaryolume of benzene, to prevent the concentration of benzene hexachloride from reach- REFERENCES CITED v u The following references are of record in the file of this patent:

J FOREIGN PATENTS Country Date Great Britain May 7, 1936 OTHER REFERENCES Stewart et a1., Jour; Am. Chem. 800., vol. 53, .pasesllZl-B (1931).

Number 

1. THE METHOD WHICH COMPRISES CIRCULATING BENZENE IN A CLOSED SYSTEM BUBBLING THEREINTO AN AMOUNT OF CHLORINE SUFFICIENT TO KEEP THE BENZENE SATURATED THEREWITH AND AN AMOUNT OF PROPYLENE SUFFICIENT TO INITIATE AND TO MAINTAIN THE ADDITION REACTION BETWEEN BENZENE AND CHLORINE, BUT NOT IN EXCESS OF ONE MOL OF PROPYLENE FOR EACH 6 MOLS OF CHLORINE, MAINTAINING THE TEMPERATURE OF THE REACTION BETWEEN 35* AND 45* C., TO PRODUCT BENZENE HEXACHLORIDE, AND CONTINUOUSLY WITHDRAWING PART OF THE CIRCULATING SOLUTION FROM THE SYSTEM AND REPLACING IT WITH A SIMILAR VOLUME OF BENZENE, TO PREVENT THE CONCENTRATION OF BENZENE HEXACHLORIDE FROM REACHING THE SATURATION POINT IN THE CIRCULATING LIQUID. 